The present application relates to a method for treating carbon nanotubes (CNTs), carbon nanotubes produced by the treatment method, and CNTs devices comprising thereof. Specifically, the present application is directed to an efficient and cost-effective separation/enrichment of CNTs of different types or properties such as semi-conducting single-walled carbon nanotubes (S-SWNTs), metallic single-walled carbon nanotubes (M-SWNTs) and chiral CNTs, and carbon nanotubes produced by the treatment method, and CNTs devices comprising thereof.
As a one-dimensional nano-material, CNTs have attracted increasing attention due to their excellent electrical, mechanical, and chemical properties. Intensive studies on the nano-material have proposed many potential widespread applications for CNTs in various fields. For example, CNTs can be applied in the fields of electronics, optics, mechanics, biotechnology, and ecology, such as, nano-field effect transistor, field emission source, hydrogen storage material, high strength fiber, and sensor.
CNTs can be classified into single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) according to the number of the wall-forming atomic layers. Specifically, MWNTs may be considered as being formed by nesting SWNTs with different diameters. Research and application in the field of CNTs have shown that SWNTs and MWNTs with relatively small number of atomic layers are of importance due to the outstanding performance.
Based on the conductivity of SWNTs, SWNTs can be further classified into M-SWNTs and S-SWNTs. M-SWNTs, for example, can be used in various devices including conductive film, field emission and the like. S-SWNTs have found their application, for example in nano-filed effect transistors, sensors and the like. However, SWNTs are generally grown as bundles of M-SWNTs and S-SWNTs, and thus the application of either M-SWNTs or S-SWNTs is limited by its proportion in the bundles. It has been theoretically determined that SWNTs are usually comprised of ⅓ proportional M-SWNTs and ⅔ proportional S-SWNTs according to the diameter and chiral angle of SWNTs (Saito R et al., Material Science and Engineering, 1993, B19: 185-191). The carbon materials produced by different process conditions and purification treatment and the like, however, do not contain M-SWNTs and S-SWNTs in the theoretical ratio of 1:2. In addition, the metallicity of CNTs gradually increases with the increase of the number of the carbon atomic walls, and finally CNTs become metallic.
The conventional methods for preparing CNTs include graphite arc-discharging process, chemical vapor deposition process, laser evaporation process, and the like. CNTs obtained by these conventional methods usually comprise bundles of M-SWNTs mixed with S-SWNTs. Therefore, in order to put M-SWNTs and S-SWNTs into their respective application field, it is necessary to separate the CNTs of different conductivity from each other. Hence, separation of CNTs has become one of the important topics in the research.
So far, many methods have been proposed to separate M-SWNTs and S-SWNTs by utilizing their differences in chemical and physical properties.
Chemical approaches have been considered to be promising routes for efficiently separating SWNTs. Some chemical/biological molecules have been demonstrated to have diameter/properties-selective to SWNTs. For example, octadodecylamine [J. Am. Chem. Soc. 2003, 125, 3370; Appl. Phys. Lett. 2004, 85, 1006] or porphyrin [J. Am. Chem. Soc. 2004, 126, 1014] have been chosen to separate S-SWNTs from M-SWNT, starting from carboxy-functionalized SWNTs. Furthermore, it is also reported that there is selectively covalent functionalization in SWNT [Science 2003, 301, 1519]. However, the pristine structure and properties of the treated SWNTs have been either damaged or degraded, resulting in a low yield of the desired product.
By utilizing the selective interaction between the pristine SWNTs and bromine, M-SWNTs have been separated from the S-SWNTs based on the density difference of the resulting samples [Nano Lett. 2003, 3, 1245]. Density-gradient ultracentrifugation has been recently proposed to be a promising process for separating CNTs of different types in accordance with their diameter, band gap and electronic characterization [Nature Nanotechnology 2006, 1, 60]. However, the separation processes are time-consuming and high cost is required for centrifugation.
It is also reported that M-SWNTs and S-SWNTs wrapped with DNA have been separated by anion exchange chromatography or centrifugation [Science 2003, 302, 1545; Nano Lett. 2004, 4, 543]. The use of anion exchange chromatography separation leads to high cost and it is required to remove the wrapping DNA from SWNTs.
Separation of SWNTs has been reported previously by utilizing the selective interaction between amino group and M-SWNTs [Chem. Phys. Chem. 2004, 5, 619; J. Am. Chem. Soc. 2005, 127, 10287]. However, time-consuming and expensive centrifugation process is also involved in the separation process.
Therefore, there exists a need for a new process for treating CNTs, which can be used to separate CNTs of different types or properties, such as M-SWNTs and S-SWNTs more efficiently, conveniently, and cost-effectively.